The evidence for evolution

Use the links above to explore the evidence for evolution from various fields of science.

A Basic Introduction


How does Science work?

  • Science is a thought process in which one reaches a tentative conclusion based on the available evidence and continues to test this conclusion.
  • Science simply shows us the most likely conclusion based on the evidence we have.
  • Millions of scientists around the world publish hundreds of thousands of research reports in the peer-reviewed literature.
  • Only findings reported in the scientific literature are taken seriously by scientists.


What is Evolution?


Evolution is a collection of facts, theories, and hypotheses

The fact of evolution

It is a fact that all known life on Earth has changed and diversified over 3.5 billion years and shares common ancestry.

The theory of evolution

It is a scientific theory that the evolution of life is largely driven by natural selection working on random mutations, with other forces such as horizontal gene transfer, symbiosis, and genetic drift also playing a role.


Fact vs Scientific Theory


Facts and scientific theories are mutually exclusive kinds of ideas

Facts

Facts state "what" happens or happened. Facts require empirical physical evidence.

Theories

Theories state "how" and "why" something happens or happened. Theories require empirical physical evidence, widespread support from the scientific community, and a natural, explained mechanism.

Developing theories is the ultimate goal of the scientific community.

Neither creationism nor intelligent design meets the requirements for either a theory or a fact.


Do scientists accept evolution?


Evolution is almost unanimously accepted by scientists around the world

Opposition to evolution in the developed world is largely US-based.

97% of US scientists accept evolution.(Pew 2009)

Acceptance of evolution amongst US scientists

How does evolution work?


Evolution is primarily driven by natural selection and random mutations

  • Organisms which are more likely to reproduce pass down their genes.
  • Genetic mutations and traits which help an organism survive are passed on.
  • Complex traits slowly arise through a series of completely functional intermediates
  • The purpose of genes and physical features changes over time.


Graphical Evolution



The History of Life


Evolution creates a bush-like pattern of organisms and has no direction

  • Evolution is not a straight line, and is not a progressive process.
  • Rather, organisms change over time and become radically different in response to their environments.
  • Below is a basic tree of life created using genetic and fossil evidence. (Ayala et al. 1998)


Have we ever observed Evolution?

Scientists have observed the evolution of new species, novel information, beneficial mutations, and complex features in organisms.

  • Several new species of Anolis lizards were observed to have evolved from an original population.(Gingerich, 1983)
  • Croatian lizards developed new, functional organs known as cecal valves to help digest a new plant diet.(Herral 2008)

  • In a controlled laboratory, beneficial mutations in yeast increased genetic information. (Brown et al. 1998)
  • A unicellular strain of algae was observed to evolve multicellularity in an experiment. (Boraas et al., 1998)

What is the evidence for Common Descent?

The evidence that evolution occurred is massive. Read about it in depth here.

The Genetic Evidence for Evolution

  • Humans share many degraded genes which used to work, but no longer do, with other animals: evidence of a long, natural past. (Nishikimi et al. 1992)
  • Humans share many almost identical genetic errors with other primates: evidence of our common ancestry. (Capozzi et al. 2009)
  • Comparing genetic sequences between species produces similar trees of relationships, like the one above.

The Fossil Evidence for Evolution


The evidence for human evolution is very apparent in the fossil record. Above is a side-by-side comparison of different hominids, showing the gradual change in the fossil record.

There are also substantially more transitional fossils from the history of life.

Read more here


Additional Resources

Learn more about evolution on our site!

Check out external resources on evolution here!

An Intro to Science

Evolution has become a general term that describes a variety of scientific facts, theories, and hypotheses which contribute towards our knowledge of the origins of life on Earth. In a strict, scientific sense, it refers to the manner in which populations change in terms of their genetic makeup over time; in a broader sense, it encompasses the ideas which describe how this happened, why this happened, how populations on Earth are interrelated, and the simple fact that life on our small 4.5 billion year old planet, which is a part of an astoundingly large 13.7 billion year old universe, shares a common ancestry. Evolution is accepted by over 97% of U.S. scientists.

So, evolution is a collection of scientific theories, hypotheses, and facts. However, what do these terms really mean? First, we must review how science itself works in order to understand how we should view these various pieces of evolutionary science. Science is, first and foremost, a thought process. Every single human being, whether subconsciously or consciously, uses this thought process thousands of times throughout the day. It is part of our legal systems, our educational systems, and is often called by the colloquial term "common sense". It is a relatively simple algorithm which we use to reach almost all ordinary decisions. It has since become standardized as the correct way of performing and publishing research in the scientific community.

The Scientific Method

1. Collect evidence.

2. Determine the position best supported by that evidence.

3. Acknowledge that this position is a temporary conclusion that is subject to change as one continues to gather additional evidence.

While there are variations on this scientific method (one formal example is shown on the left above), essentially, the process involves collecting evidence, determining the position best supported by that evidence, and acknowledging that this position is simply a very temporary conclusion that is subject to change as one continues to gather additional evidence. We make the vast majority of our decisions using such rational thought; it is instinctive to do so.

It is important to note that skepticism is the default position of the rational thought process. All ideas which are not supported by the physical evidence collected are rejected, not as false, but as scientifically false: there is a small but negligible possibility that these are in fact true, but because they have not passed the test of rationality, they must be rejected.

On the converse, all ideas which are supported by the physical evidence collected are accepted, not as true, but as scientifically true; there is a small but negligible possibility that these are in fact false, but because they have passed the test of rationality, they must be accepted. "Absolutely true" and "Absolutely false" are used only in theological absolute positions.

This is, of course, considered common sense, as rationality itself is already ingrained into us. Everyone acknowledges the remotely small possibility that facts are false and falsehoods are fact. However, one does not accept these remote possibilities as true, and this is the key to understanding rationality. If one did so, of course, one would end up being forced to hold a literally infinite number of equally preposterous and ludicrous positions.

Thus, we can define the discussed terms as such:

Fact: A fact is an idea which states, any statement with strong empirical evidence behind it. Facts are, of course, temporary conclusions that may change on the discovery of more evidence.

Theory: A scientific theory is an idea with powerful empirical evidence and strong scientific support which explains; theories provide the answers to "How" and "Why" questions with proposed explanatory mechanisms. A theory is not weaker than a fact in any way other than that the cause behind a correlation can be difficult to support; this aside, theories are merely a different kind of idea.

Hypothesis: A hypothesis is an idea which also seeks to explain, but differs from the theory in that it does not necessarily have powerful empirical evidence or a community behind it. Hypotheses range from widely accepted to highly tentative and we dismiss and introduce them constantly throughout our lives.

We have listed some of the facts of evolution, the theory of evolution, and the hypotheses of evolution below alongside examples from other fields for comparison.

Facts


GravityThe Ancient EgyptiansCommon Ancestry
Objects fall to the ground. The Ancient Egyptians existed. Life on Earth shares common ancestry.

Note that all of these facts are merely statements supported with empirical evidence; we can be relatively sure that they are true, but, of course, there's a very small chance that they are not. This is how science works; all positions are questionable.

Theories


Germ TheoryAtomic TheoryThe Theory of Evolution
Microorganisms are the cause
of many diseases.
Matter is composed of
atoms.
Life evolves by natural selection
working on random mutation along
with other natural forces.


Hypotheses


The Red Queen HypothesisLimestone Concrete HypothesisPostural feeding hypothesis

An organism must continually adapt in order to survive in an ecosystem.

The pyramids were built with limestone concrete. Bipedalism evolved in hominids to help reach hanging fruit.

When a scientist or rationalist claims to "believe" in evolution, he or she is using the term in a colloquial manner rather than the meaning it has in a religious context; in other words, he or she simply accepts evolution as the best explanation we currently have, based on the physical evidence, for the origin of species.

Now that the reader has a firm understanding of both the concept of science and the difference between various types of ideas, we can briefly describe the actual specifics of the various components of evolution.

Common Descent

Common Descent is the simple fact that all life on our planet shares a common evolutionary ancestor. This fact is supported by a vast amount of empirical evidence; see the links at the top of this page for examples. It is also nearly unanimously accepted throughout the scientific community.

The Ages of the Earth and Universe

Our Universe is old. Very, very old. Approximately 13.7 billion years old, based on precise measurements from several different sources. Other sources, while not specific, also confirm minimum ages on the Universe.

For more on how the age of the Universe is determined, see our page here

Our Earth is not as old as our universe. In fact, it has formed relatively recently, as has the rest of our solar system. According to dates from several independent radiometric tests, our Earth is approximately 4.54 billion years old. A close match with helioseismological data solidifies this date. Similarly to our universe, a host of other methods also scientifically confirm that the Earth is extremely old.

For more on how the age of the Earth is determined, see our page here

Evolutionary Theory

The basis of the theory of evolution was first developed by Charles Darwin in the 19th century. Darwin published his results alongside those of Alfred Wallace, another scientist who had developed highly similar ideas around the same time. It is important to remember that Charles Darwin was responsible for popularizing the basis for the modern theory of evolution, and not for the idea of common descent. Common descent itself predates Darwin by about 100 years.

Darwin's theory of evolution was a basic and elegant explanation of how diversity in life arose. In other words, the theory of evolution provides the how and why behind the fact of common descent.

The modern theory of evolution is very different from what Darwin envisioned, although the basic principle of natural selection has remained the same. Since Darwin, scientists have discovered many biological and ecological forces which also contribute towards evolution, including genetic drift, horizontal gene transfer, epigenetics, transposons, retroviruses, gene duplication, and more.

Read more about how evolution works